1. Field of the Invention
The present invention relates to stowage box devices designed to safely accommodate inflatable harness-type aircraft crew masks equipped with a harness-inflation comfort control feature. The boxes of the invention prevent mask storage in a condition with the comfort control feature enabled, so as to preclude a situation where the mask is not rapidly donnable in a stowed, putatively "ready" condition. More particularly, the invention pertains to such stowage boxes including strategically located stop and containment structure rendering it effectively impossible to store the switchable comfort control masks in the switch-on comfort control position.
2. Description of the Prior Art
Safety considerations and governmental regulations prescribe that flight crew oxygen masks should be constructed to enable the mask to be quickly donned (within a few seconds) using only one hand. Donning the mask in this manner during an emergency situation allows the wearer to use the remaining hand to attend to the aircraft controls. To enable quick donning, storage of the mask is normally provided within close proximity to a crew member's seat for one-handed access by the user. For example, the stowage box could be mounted on the floor of the cockpit or on the cabin wall adjacent the crew member.
Quick-donning inflatable head harnesses for flight crew oxygen masks are known in the art and typically comprise an expandable harness or strap having ends attached to the mask. The harness includes a manually operated valve which controls delivery of pressurized air through the harness for inflation thereof. Upon opening of the valve, pressurized air causes rapid expansion of the harness to a somewhat rigid, self-sustaining, enlarged orientation. The valve also serves to automatically vent the pressurized air and thereby deflate the harness completely once the harness and mask have been properly donned by the wearer and the valve is released. After such deflation has occurred, the inherent resiliency of the harness firmly pulls the mask around the nose and mouth areas of the wearer's face. In this manner, the mask remains tightly secured against the wearer's face in order to prevent leakage of oxygen around the periphery of the mask.
If the aircraft is flying at high altitudes and suddenly experiences rapid decompression, the flight crew mask must be pressurized in order to force air into the wearer's lungs. In this situation, the harness must exert rather significant forces urging the mask against the wearer's face in order to overcome the pressure of the oxygen flowing within the mask. However, it has been found that substantial discomfort and fatigue to the wearer are experienced when wearing such tightly fitting masks over long periods of time.
Adjustable crew mask comfort control systems are known in the art as a means for effectively alleviating discomfort which can be caused by the full deflation of a pneumatically expandable mask harness. Such comfort adjustment systems typically comprise a valve mechanism that allows only partial deflation of the harness once the valve is released and also serves to slowly reinflate the harness to a limited extent in order to slightly diminish the tension or "pull" caused by the deflated harness. One such design, as described in French Patent No. 2,614,208, includes a valve mechanism having an external comfort control switch with at least two positions. In the switch-on or "comfort" position, the user can manually adjust the valve to enable only partial deflation to a certain comfort level after full inflation of the harness is achieved optimum comfort is obtained. In the switch-off or "emergency" position, operation of the mask is identical to that of the mask without the comfort adjustment system, and full and quick inflation of the harness is therefore permitted for rapid donning, while full deflation of the harness will occur once the valve mechanism is released.
It will be appreciated that if the mask is not being worn, it should be stored with the comfort control switch in the switch-off or the "emergency" position. If the mask is instead stored in the switch-on or "comfort" position, the harness would not be subjected to full inflation pressure upon retrieval and the user would be unable to quickly and easily don the mask using one hand. To avoid that situation, a stowage box for holding the crew mask should be constructed to allow insertion of the mask therein only if the control switch is in the switch-off or "emergency" position. However, despite attempts to create a stowage box that provides such safety measures, experience has proven that stowage of the crew mask with the control switch in the switch-on or "comfort" position still occurs regularly notwithstanding such specially constructed stowage boxes including to prevent such improper stowage.